Devices such as, for example, the devices used for space missions may be subjected to various stresses due to the environment in which they are located.
For example, phenomena due to accumulation of radiation, or TID (Total Ionizing Dose), can increase the current consumption of the electronic circuits, or even of entire systems, exhausting the energy resources present in a satellite in a short time, resources which are difficult to regenerate during the mission. The impact of heavy ions (a single event transient—SET) can generate current peaks in the devices downstream of the power supplies, in such a manner as to damage the devices themselves, to alter the current consumption or to create short-circuits, also with some important consequences.
A current limiter may be considered as an intelligent fuse. The purpose of a fuse can be to protect a power supply and/or a load from detrimental effects due, for example, to a short-circuit or to an excessive current demand by a load.
A fuse may prove to be too slow with a reaction time that is insufficient to guarantee the integrity of the system, with a risk of damaging devices or parts of the system.
A current limiter may thus be seen as an “intelligent” fuse which exhibits a negligible impedance under normal operating conditions and switches into a high impedance state when the current flowing through it exceeds a programmed limiting level.
A fast reaction time of the current limiter reduces the probability of damaging the downstream devices from the first moments of the onset of the fault, for example because it limits the current, thus reducing the stress on the components.
After the fault has been repaired, the current limiter (if programmed appropriately) may be able to spontaneously return to the low-impedance state even without a recovery intervention.
When the current limiting circuit is in operation, various solutions may provide for the voltage across the terminals of a sense resistor Rsense to supply information on the value of the current (Isense) flowing through the load.
The voltage VRsense across the terminals of the resistor Rsense may be compared with a voltage reference, for example fixed, by means of an operational amplifier which drives, for example, a control electrode (for example, the gate) of a power transistor (for example, a power p-channel MOS (PMOS) transistor) biasing it into a triode region or into an active region, respectively, in the case of a typical operation of the system or under current limiting conditions.
In such a solution, the current limiting value ILIM may be imposed by the balancing (of voltage) between the voltage drop across the terminals of Rsense and the voltage reference at the input of the operational amplifier (High Voltage), for example according to a relationship of the type:ILIM=Voltage Reference/Rsense
When the load demands a value of current higher than the programmed limiting value, the voltage across the terminals of the resistor Rsense tends to become larger than the voltage reference, the negative feedback loop acts in such a manner that the output of the operational amplifier increases the gate potential of the Power PMOS in such a manner as to determine the situation of equilibrium in which the system draws the maximum programmed limiting current ILIM. In this new condition of equilibrium, the voltages VRsense and reference equalize and the output of the operational amplifier can drive the gate of the Power P_MOS from the linear region to the saturation region.
U.S. Pat. Nos. 7,245,113 and 7,728,655 (incorporated by reference) show examples of the above.
Despite the extensive activity in the sector, there is still a need to provide improved solutions for current limiters.